Human Chromosomes- what you know… • Humans have 46 chromosomes (diploid-2N) • 2 of them are sex chromosomes (X and Y) they determine what sex you are • XX = female • XY = male • 44 of them are autosomes they do not determine the sex of an individual. Sex chromosomes
How is a KARYOTYPE Made? • Collect sample: • Fetus: amniotic fluid collected during an amniocentesis or a piece of the placenta collected during a chorionic villi sampling test (CVS). • Newborn: white blood cells • Separate dividing & non-dividing cells using chemicals • Culture the dividing cells to get a lot of cells • Add chemical to stop cell division when chromosome is compacted • Lyse the cells • Stain the chromosomes (stain sticks to regions with a lot of “A” and “T” bases • Analyze!
How is a KARYOTYPEAnalyzed? • Use computers to match the homologous pairs. • We will cut out the chromosomes from a chromosome spread then arrange them to match the banding patterns of the homologous pairs • Use banding patterns, size of chromosome, and position of centromere • This type of picture is called a KARYOTYPE
What does a Karyotype tell you? • Sex (male or female) • Irregular numbers of chromosomes • Any mutations in the chromosomes • Basically: all the chromosomes in a cell are displayed and can be examined for abnormalities
Chromosomal Disorders • Most of the time, the mechanisms that separate human chromosomes in meiosis work very well, but things can go wrong • The most common error: NONDISJUNCTION • The chromosomes fail to separate in Anaphase I or II • The result? Abnormal numbers of chromosomes in gametes.
Nondisjunction Prefixes: dis = absence of / opposite of non = not Root Word: Junction = joining together • disjunction = the act of separating • nondisjunction = the act of not separating
Metaphase I Figure 14-15 page 352 “Trisomy” = 3 copies of a chromosome Nondisjunction (after anaphase I) End of Meiosis—4 gametes produced
Examples of Chromosomal Disorders • Down Syndrome (3 #21 chromosomes) • Klinefelter’sSyndrome (XXY) • Turner’s Syndrome (XO) • Triple X Syndrome (XXX)
Examples of Nondisjunction resulting in Chromosomal Disorders • Down's Syndrome: 47 chromosomes with 3 #21 chromosomes. • Triple-X Syndrome: 47 chromosomes caused by 3 X chromosomes. • Klinefelter's Syndrome: 47 chromosomes caused by 2 X chromosomes and 1 Y chromosomes. • Turner's Syndrome: 45 chromosomes with 1 X chromosome (caused by the absence of one of the X chromosomes or a Y chromosome).
Chromosomal Mutations • Chromosomal Mutations • Deletion • Duplication • Inversion • Translocation
Chromosomal Mutation (change in number) • If an organism is born with the incorrect number of chromosomes • Ex: 47 human chromosomes instead of 46 • Result of nondisjunction
Down Syndrome • 3 copies of chromosome #21 • 1 in 800 babies in the US is born with this disease • produces mild to severe mental retardation • May not live as long
Klinefelter’s Syndrome • This is a sex chromosomal disorder associated with males. • Nondisjunction causes an extra X chromosome to be passed along during meiosis (XXY). • Resulting male cannot reproduce • Cases have been found in which individuals were (XXXY) or (XXXXY) • Decrease muscle mass and body hair
Turner’s Syndrome • This is a sex chromosomal disorder associated with females. • Nondisjunction causes offspring to inherit only one X chromosome (genotype = XO). • Resulting female is sterile due to underdeveloped sex organs. • 1/2500 females
Review question..Who determines the sex of a child? The mother or the father? THE FATHER!!!! Why?
Why does the father determine the sex of the offspring??? • Mom is XX: she can donate either one X chromosome or the other X chromosome to the offspring (mom can only donate an X) • Dad is XY: he can donate either an X chromosome or a Y chromosomes. • If the offspring receives an X from dad, it is female • If the offspring receives a Y from dad, it is male